In what could be absolutely considered a glittering example of exactlywhy golden keys offering a backdoor into secure services shouldn’t exist, Microsoft accidentally leaked the master key to their Secure Boot system.

The leak potentially unlocks all devices with Microsoft Secure Boot technology installed, stripping their locked operating system status, enabling users to install their own operating systems and applications in place of those designated by the Redmond technology behemoth.

The leak shouldn’t compromise your device security — in theory. But it will open the lines for alternative operating systems and other applications that would previously have failed to work on a Secure Boot system.

How will Microsoft respond to this? A simple update to alter each Secure Boot base key? Or is it simply too late, damage done?

Let’s take a good look at what the Secure Boot leak means for you and your devices.

What Is Secure Boot?

“Secure Boot helps to make sure that your PC boots only using firmware that is trusted by the manufacturer”

“Should this stand, we can envisage OEMs building machines that will offer no easy way to boot self-built operating systems, or indeed, any operating system that doesn’t have appropriate digital signatures.”

While there are undoubtedly numerous desktops and laptops for sale with unlocked UEFI settings, this could prove to be another stumbling block for those wishing to try an alternative to their Windows operating system.

Yet another road block for Linux advocates to work around… sigh.

And Now Secure Boot Is Permanently Unlocked?

Permanently, I’m not so sure. But for the meantime, Secure Boot can be unlocked. Here is what happened.

I know I’ve been referring to a super-duper skeleton-type key that unlocks every single lock in the entire Microsoft UEFI Secure Boot universe… but it actually comes down to which policies you have signed on your system.

“During the development of Windows 10 v1607 ‘Redstone’, MS added a new type of secure boot policy. Namely, “supplemental” policies that are located in the EFIESP partition (rather than in a UEFI variable), and have their settings merged in, dependant on conditions (namely, that a certain “activation” policy is also in existance, and has been loaded in).

Redstone’s bootmgr.efi loads “legacy” policies (namely, a policy from UEFI variables) first. At a certain time in redstone dev, it did not do any further checks beyond signature / deviceID checks. (This has now changed, but see how the change is stupid) After loading the “legacy” policy, or a base policy from EFIESP partition, it then loads, checks and merges in the supplemental policies.

See the issue here? If not, let me spell it out to you plain and clear. The “supplemental” policy contains new elements, for the merging conditions. These conditions are (well, at one time) unchecked by bootmgr when loading a legacy policy. And bootmgr of win10 v1511 and earlier certainly doesn’t know about them. To those bootmgrs, it has just loaded in a perfectly valid, signed policy.”

It doesn’t make good reading for Microsoft. It effectively means the debug-mode policy designed to allow developers – and only developers – chance to negate the signing processes is open to anyone with a retail version of Windows 10. And that that policy has leaked onto the Internet.

Remember The San Bernardino iPhone?

“You can see the irony. Also the irony in that MS themselves provided us several nice “golden keys” (as the FBI would say ;) for us to use for that purpose :)

About the FBI: are you reading this? If you are, then this is a perfect real world example about why your idea of backdooring cryptosystems with a “secure golden key” is very bad! Smarter people than me have been telling this to you for so long, it seems you have your fingers in your ears. You seriously don’t understand still? Microsoft implemented a “secure golden key” system. And the golden keys got released from MS own stupidity. Now, what happens if you tell everyone to make a “secure golden key” system? Hopefully you can add 2+2…”

For those encryption advocates this has been an all-to-bittersweet moment that will hopefully provide some well needed clarity for law enforcement agencies and government officials alike. Golden backdoors will never stay hidden. They will always be discovered, be that by an unforeseen internal vulnerability (Snowden revelationsHero or Villain? NSA Moderates Its Stance on SnowdenHero or Villain? NSA Moderates Its Stance on SnowdenWhistleblower Edward Snowden and the NSA's John DeLong appeared on the schedule for a symposium. While there was no debate, it seems the NSA no longer paints Snowden as a traitor. What's changed?Read More) or by those interested in poking and pulling technology and its underlying code apart.

The Ball Rests With Microsoft

As I mentioned, this shouldn’t really pose a massive security risk to your personal devices, and Microsoft released a statement downplaying the relevance of the Secure Boot leak:

“The jailbreak technique described in the researchers’ report on August 10 does not apply to desktop or enterprise PC systems. It requires physical access and administrator rights to ARM and RT devices and does not compromise encryption protections.”

As well as this, they have hastily released a Microsoft Security Bulletin designated “Important.” This will resolve the vulnerability once installed. However, it won’t take much to install a version of Windows 10 without the patch implemented.

Golden Keys

Unfortunately, this is unlikely to lead to a new glut of Microsoft devices running Linux distros. I mean, there will be some enterprising individuals who take the time test this, but for the majority of individuals, this will simply be another security blip that passed them by.

It shouldn’t.

Not giving a damn about Linux distros on Microsoft tablets is one thing, sure. But the wider implications of a golden key leaking into the public domain to unlock potentially millions of devices is another.

A couple of years ago The Washington Post made a rallying call for “compromise” on encryption, proposing that while our data should obviously be off-limits for hackers, perhaps Google and Apple et al should have a secure golden key. In an excellent critique of exactly why this is a “misguided, dangerous proposal,” Keybase co-creator Christ Coyne explains, quite plainly, that “Honest, good people are endangered by any backdoor that bypasses their own passwords.”

Gavin is the Technology Explained Editor, as well as a Security and Windows regular. He has a Contemporary Writing degree pillaged from the hills of South Devon, but now resides in the deepest depths of Cornwall, calling Penzance his home. In a 10-year writing career he has covered real estate,…